Planar lipid bilayer platforms are widely used in the study of ion channels. As opposed to techniques involving the isolation of ion channels over patches of live cells, planar lipid bilayer platforms are engineered systems that allow for greater levels of control over the membrane environment surrounding reconstituted ion channels. They also allow for superior control over the aqueous compartments adjacent to the membrane.
In spite of these advantages, artificial lipid bilayers are characterized by shortcomings of fragility and short lifetime and the necessity for a human operator to form them at the time and place of use. This is typically a very low throughput one-off process, which has significantly limited their technological prospects. Yet, if these shortcomings of traditional bilayer platforms can be reduced, specifically the expertise required to perform experimentation and increased experimental throughput, artificial planar bilayers can function as a useful tool in the study of ion channels.
Using the contacting monolayer (CM) method (Poulos, J, “Ion channel and toxin measurement using a high throughput lipid membrane platform,” Biosensors & Bioelectronics, 24:1806-1810, 2009), which is incorporated by reference herein in its entirety, planar lipid bilayers can be formed. The CM method involves the mechanical contacting of two individual lipid monolayers, thereby forming a bilayer.
When an aqueous droplet is placed in an organic solvent and either liquid contains dissolved lipid molecules, the lipids will self-assemble at the aqueous/organic interface, forming a monolayer. Production of a lipid bilayer is possible if two such monolayers are mechanically brought into contact. Recently, this method was used in microfluidic systems for bilayer formation. Bilayers were formed by extracting the organic solvent through the device, or by contacting the aqueous phases by applying pressure. In addition to this, a version of this method created networks of bilayers by combining them with a micromanipulator. The CM method was also adapted to a vertical orientation, where a droplet was placed on a hydrogel support and used to track single molecules optically. These methods used manual manipulation of the phases to create bilayers.
Electrical measurement of ion channels involves electrical access to each side of the bilayer in which the ion channels are inserted. For artificially formed bilayers, this involves placing an electrode in the aqueous solutions on each side of the bilayer. However, placement of the electrode can perturb one or both of the aqueous solutions sufficiently to disturb or destroy the bilayer. The bilayer can be reformed by manipulating the position of the electrode, but this compromises the high throughput of the bilayer formation process.
In the work of Ide et al. (Anal Chem, 2008. 80(20): p. 7792-5), which is incorporated by reference herein in its entirety, one half of the bilayer-forming aqueous solution was made from a hydrogel. An electrode was insertable into the hydrogel without compromising the bilayer. Although this may appear to address the concerns associated with the compatibility of electrical measurement with high throughput bilayer formation, if there is an analyte or protein solution in the hydrogel, the hydrogel should be exchanged for a subsequent measurement. This would necessitate the prior synthesis of a large amount of hydrogel-filled capillaries which would need to be exchanged for high throughput bilayer formation.
Therefore, there remains a need for methods and compositions that overcome these deficiencies and can increase the degree of throughput in lipid bilayer formation and measurement.